VOLUNTEER RR CORN MANAGEMENT ROUNDUP READY SOYBEAN CORN ... · Volunteer RR ®corn management in roundup ready ... management practices were carried out using the herbicides previously

Planta Daninha, Viçosa-MG, v. 33, n. 1, p. 119-128, 2015

119Volunteer RR®corn management in roundup ready® soybean-corn ...

1 Recebido para publicação em 26.8.2014 e aprovado em 22.9.2014.2 Universidade Federal de Mato Grosso, Sinop-MT, Brasil; <[email protected]>; 3 Embrapa Tabuleiros Costeiros, Aracajú-SE,Brasil; 4 Embrapa Milho e Sorgo, Sete Lagoas-MG, Brasil.

VOLUNTEER RR® CORN MANAGEMENT IN ROUNDUP READY® SOYBEAN-CORN SUCCESSION SYSTEM1

Manejo do Milho RR® Voluntário em Sistema de Sucessão Soja-Milho Roundup Ready

PETTER, F.A.2, SIMA, V.M.2, FRAPORTI, M.B.2, PEREIRA, C.S.2, PROCÓPIO, S.O.3, andSILVA, A.F.4

ABSTRACT - The present study evaluated the effects of cover crops (Pennisetum glaucum,Crotalaria spectabilis and Urochloa ruziziensis) associated with the application of herbicides{glyphosate; (glyphosate + haloxyfop-R); (glyphosate + fluazifop-p-butyl); (glyphosate +imazethapyr) and (glyphosate + imazaquin)} in soybean desiccation management forvolunteer RR® corn control. The experiment was conducted under field conditions at Sinop-MT, during the 2013/2014 crop season, in a randomized complete blocks design with factorialscheme and four replications. The following parameter were evaluated: dry matter of covercrops and ground coverage rate, control of volunteer RR® corn present at the time ofdesiccation, dry matter, height and intoxication level on soybean plants caused by herbicidesat 7, 14 and 28 days after emergence (DAE), control of volunteer RR® corn derived fromemergence fluxes subsequent to desiccation management and soybean yield. The jointapplication of (glyphosate + haloxyfop-R) provided the best level of volunteer RR® corn controlpresent at the time of desiccation. Satisfactory control (80%) of volunteer corn was obtainedwith the application of (glyphosate + imazethapyr). This treatment displayed an additionalresidual effect of imazethapyr, which efficiently controled volunteer RR® corn derived fromfluxes subsequent to desiccation management, especially in treatments performed underU. ruziziensis straw. None of the herbicides used in desiccation management caused anysignificant effect on dry matter, height and phytotoxicity of soybean plants at 7, 14 and28 DAE nor on grain yield.

Keywords: Zea mays, Glycine max, cover crops, herbicides.

RESUMO - Avaliaram-se nesta pesquisa os efeitos de plantas de cobertura (Pennisetum glaucum,Urochloa ruziziensis e Crotalaria spectabilis) associadas à aplicação de herbicidas {glyphosate;(glyphosate+haloxyfop-R), (glyphosate+fluazifop-p-butil), (glyphosate+imazethapyr) e(glyphosate+imazaquin)} no manejo de dessecação na cultura da soja, visando o controle do milhoRR® voluntário. O experimento foi conduzido em campo no município de Sinop-MT, na safra 2013/2014, no delineamento experimental de blocos casualizados, em esquema fatorial, com quatro repetições.Foram avaliados: matéria seca das plantas de cobertura e cobertura do solo, controle do milho RR®

voluntário presente no momento da dessecação, matéria seca, altura e intoxicação das plantas desoja pelos herbicidas aos 7, 14 e 28 dias após a emergência (DAE), controle do milho RR® voluntáriooriundo de fluxos de emergência posterior ao manejo de dessecação e produtividade da soja. Aaplicação conjunta de (glyphosate+haloxyfop-R) proporcionou o melhor nível de controle do milho RR®

voluntário presente no momento da dessecação. Controle satisfatório (80%) do milho voluntário foiobtido com a aplicação de (glyphosate+imazethapyr). Este tratamento teve como adicional o efeitoresidual do imazethapyr, que controlou de maneira eficiente o milho RR® voluntário oriundo de fluxoposterior ao manejo de dessecação, principalmente nos tratamentos cultivados sob palhada deU. ruziziensis. Não houve efeito significativo dos herbicidas utilizados no manejo de dessecaçãona matéria seca, altura e fitotoxicidade das plantas de soja aos 7, 14 e 28 DAE e na produtividade degrãos.

Palavras-chave: Zea mays, Glycine max, plantas de cobertura, herbicidas.

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INTRODUCTION

The State of Mato Grosso currentlyoccupies a prominent position in terms ofgrain production, with an area planted tosoybean (Glycine max) and corn (Zea mays) of8.62 and 3.28 million hectares respectively,representing 28.6 and 20.8% of the total areaof these crops in the country (CONAB, 2014).

Since its introduction in Brazil,soybean and corn planting has undergoneseveral changes, such as modifications inmanagement techniques. Among theinnovations included in the technologicalpackage are the no-till system (NTS) and theintroduction of RR® transgenic soybean andmaize. The first one endorses the preservationand maintenance of the physical, chemicaland biological characteristics of the soil by theformation of straw, crop rotation and no soildisturbance. The second aims at the use ofthe post-emergence herbicide glyphosate,controlling weeds in soybean and corn crops.

According to Petter et al. (2007), with theauthorization for Roundup Ready® soybeancultivars planting in Brazil, the intensity ofglyphosate use at planting, which was alreadygreat due to the applications for desiccationmanagement, became even greater with thepossibility of performing post-emergenceapplications. Recently, the use of this herbicidehas conquered more and more of the marketafter the release of commercial-scale plantingof maize resistant to glyphosate. In sensitiveplants, glyphosate inhibits the activity ofthe key enzyme (5-enolpyruvylshikimate-3-phosphate synthase –EPSPs) (Zuffo et al.,2014) of aromatic amino acids tryptophan,phenylalanine and tyrosine synthesis process.

Given the characteristics of glyphosate,which is the only one that has this mechanismof action, and with continued use of thisherbicide in corn-soybean succession croppingsystem, there is need for a proper chemicalweed control; otherwise, an increase ofselective pressure and the emergence of fasterherbicide-resistant weeds may occur. Thecultivation of these two crops is closelyassociated, since that in regions where thereis a better rainfall distribution pattern,soybeans are typically grown in the summerharvest, and corn during the off-season.

In this sense, it has been observed inthe field, in addition to resistant weedpopulations, the occurrence of volunteer RR®corn derived from the previous off-season amidsoybean crops in the subsequent summerharvest. This situation has been observed inseveral regions where the succession systemand/or the soybean-corn rotation system arepredominant. This fact has hampered themanagement of soybean production, sincethat there is an intraspecific competitionwith maize, besides impairing post-harvestoperations, thus resulting in grain lossesduring this process.

Confronted with the difficulty in theherbicide portfolio that meets, in anassociative manner, the needs of both cropsand due to the undesirable effects of volunteercorn plants in soybean plantations, manyfarmers are already using soybean/cornconventional varieties. Some herbicides, asdiclosulam, that could play a preventively rolein the control of volunteer corn may havephytotoxic effect on maize in the off-seasonwhen applied in desiccation management forsoybean plantation (Artuzi & Contiero, 2006;Dan et al., 2011).

If we consider that for grain producerschemical control is the main form ofweed management, it becomes clear that itis necessary to obtain information onthe potential of sustainable and economictechniques that can be applied in theintegrated weed management, like thebenefits of no-till farming with the presenceof dry matter of cover crops on the soil surface(Gimenes et al., 2011). Thus, one alternativeis to combine the use of herbicides with covercrops management.

Dry matter production and soil coverageprovided by cover crops are factors that canhelp control weeds by physical and chemicalprocesses (allelopathy) (Pacheco et al., 2013b;Petter et al., 2013). The physical effect ofmulch helps to shade the soil, inhibitingseed germination and infestation of sometroublesome weeds, thus allowing the crop todevelop free of initial competition (Queirozet al., 2010). This effect may be extended tovolunteer corn, providing effective preventivecontrol of those plants in soybean crops.However, responses obtained with the use of



plants for soil coverage and the production ofdirect effects on weed and corn germinationdepend on the species, quantity anddistribution of residues (Chauhan et al., 2012).

Therefore, the objective of this work wasto evaluate the effects of herbicides associatedwith cover crops in desiccation management,aiming at a chemical and cultural volunteerRR® corn control in soybean crops in apreventive manner.

MATERIALS AND METHODS

The field experiment was conducted at theFederal University of Mato Grosso, Sinopcampus, during the 2013/2014 season, whosegeodetic location is 11o51’52" latitude,55o29’03" longitude and altitude of 374 m, onsoil classified as dystrophic Yellow Oxisol(“Latossolo Amarelo distrófico”, or LAd)(Embrapa, 2013). Soil textural analysis at 0-20 cm revealed 540 g kg-1 of clay content,56 g kg-1 of silt, and 400 g kg-1 of sand. Soilchemical properties are presented in Table 1.

The climate is Aw, according to Köppenglobal climate classification, characterized bytwo distinct seasons: a dry season from Mayto September, and a rainy season from Octoberto April.

We used a randomized complete blocksexperimental design, in a 3 x 5 factorialscheme, with three cover crops (Pennisetumglaucum, Urochloa ruziziensis and Crotalariaspectabilis), five herbicides [glyphosate(1,080 g ha-1); glyphosate (1,080 g ha-1) +haloxyfop-R (260 g ha1); glyphosate (1.080 g ha-1)+ fluazifop-p-butyl (187 g ha-1); glyphosate(1,080 g ha 1) + imazethapyr (106 g ha-1);

glyphosate (1,080 g ha-1) + imazaquin(160 g ha-1)], and four replications. Each plotconsisted of 4 m wide and 5 m long. For anuseful area, 0.5 m on each side of the plot and0.5 m at the ends were discarding, with a totalfloor area of 12 m².

The cover crops were grown after cornharvest, i.e. during the off-season, to serve asstraws in a subsequent soybean desiccationmanagement (2013/2014 season) and tocontrol volunteer RR® corn and weed presentin the growing areas. AG 7088RR maizecultivar was sown during the off-season, inFebruary 2013, at density of 60,000 plants ha-1,with 0.6 m spacing between the lines. Inthis off-season cropping system, the samecover plants were sown, aiming at theformation of straw for the 2013/2014 season.Afterwards, in November of 2013, desiccationmanagement practices were carried outusing the herbicides previously described.Seven days after desiccation management,soybeans of TMG 2183 IPRO RR® cultivar weresown (season 2013/2104), with 0.5 m spacingbetween the lines, depth of 2-3 cm andplanting fertilization with 500 kg ha-1 ofNPK 00-20-18 fertilizer, was conducted.

At 7, 14 and 28 days after soybeanemergence (DAE) or equivalent to 21, 35 and49 days after herbicide application (DAA),the dry matter of cover crops, dry matter,height and phytotoxicity to soybean crop, andvolunteer RR® corn control at the time ofdesiccation were determined. Dry matter ofcover crops was determined according to themethodology proposed by Crusciol et al. (2005),using an iron square sized 50 x 50 cm(0.25 m²), in which the aerial part and residues

Table 1 - Chemical composition (0-20 cm) of the soil in the experimental area before the experimental installation. Sinop-MT, harvest2013/2014

M.O.: organic matter; V%: basis saturation; CTC: cation exchange capacity.1/ 2/ 3/

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of cover crops are collected through threesampling points per subplot. Soybean drymatter was determined through collecting fiveplants per plot which, as the cover cropsmatter, were taken to a forced ventilation ovenat 65 oC for 72 hours. Plant height wasevaluated by measuring from the lap to thesummit of the apical meristem. For the controlof volunteer RR® corn in soybean crops, noteswere assigned according to a percentage scalethat ranges from zero to 100, where zeromeans no plants and 100 means total presenceof the plants; a witness that received onlyglyphosate was the main parameter. In orderto evaluate the occurrence of phytotoxicitysymptoms, a visual assessment was carriedout using a percentage scale of notes, wherezero (0) represents the absence of symptomsand one hundred (100.0) represents death ofall plants of that plot.

At 28 DAE soybean, the ground coveragerate provided by cover crops was determinedwith the use of a square iron sized 0.5 x 0.5 m(0.25 m²) and a string network spaced 5 cmforming ten points, in which one observes thepresence or absence of coverage provided byplant residues in each of the sampling points(Sodré Filho et al., 2004). At 50 DAE soybean,we observed (as previously described) avolunteer RR® corn control derived ofemergence fluxes following desiccation,therefore, the residual effect of the herbicide.At the time of soybean harvest, we determinedthe grain yield in useful area of each plot, onthe basis of 13% moisture content.

After collection and tabulation of data,we performed the analysis of variance, andthe means of the significant variableswere grouped by Scott-Knott test at 5% ofsignificance with the statistics programSisvar. As for analysis on phytotoxicity andcontrol, data were subjected to arcsinetransformation (x+1)0.5; however, the valuespresented are the original means.

RESULTS AND DISCUSSION

Regardless of evaluation period, herbicidesused in desiccation management did notaffect the dry matter of cover crops (Table 2).Differences in dry matter were observed onlyamong cover crops species at 28 DAE soybean,

especially P. glaucum and U. ruziziensis, thatdisplayed 104% and 187%, respectively, highervalues for dry matter when compared toC. spectabilis. These data corroborate thoseof Carneiro et al. (2008) and Pacheco et al.(2013a), who found that dry matter productionof P. glaucum and U. ruziziensis is higher thanthat of C. spectabilis.

We can note that, after desiccationmanagement, the dry matter of C. spectabilismarkedly decreased, with 2,722 kg ha-1 at49 DAD, equivalent of only 42% of the initialdry matter measured at 21 DAD (Table 2). Thisdrastic loss of C. spectabilis dry matter is dueto the decomposition of plant residues, whichhave low C/N ratio. Additionally, this aspectgains importance as, in this region, the soilorganic matter (SOM) mineralization ratereaches high levels in residues decompositiondue to the high temperature and microbialactivity, reducing the amount of thesecompounds in the soil (Pacheco et al., 2011).It is important to highlight that this dry matterloss coincides with the onset of the total periodto prevent weed interference (Nepomucenoet al., 2007), at which the maximum drymatter accumulation on the soil wouldbe desirable, thereby targeting a possiblesupressing effect on weeds and volunteer corn.

The ground coverage rate at 49 DADfollowed the same trends as dry matter,with the highest values for P. glaucum andU. ruziziensis, which displayed 78% and 99%ground coverage rates, respectively (Table 3).Similar results were observed by Pachecoet al. (2008), who found that, under normalcerrado conditions, the ground coverage ratewas 84% and 100% for P. glaucum andU. ruziziensis, respectively, at 60 DAD.

Despite the lack of significant differencein dry matter production of P. glaucumand U. ruziziensis at 49 DAD, the same wasnot true for the ground coverage rate, wherethe highest values were observed forU. ruziziensis, with a ground coverage rate27% higher than P. glaucum. This fact isrelated to the morphological and physiologicalcharacteristics of the two species. WhileP. glaucum accumulates most of its dry matterin the stem, U. ruziziensis directs theaccumulation of dry matter to the leaves (Petteret al., 2013). Thus, those results attest to the



greater efficiency of Urochloa in groundcoverage, as it was verified by Timossi et al.(2007), whereas P. glaucum may be moreefficient in maintaining residues on the soilsurface.

According Petter et al. (2013), the distinctpatterns of dry matter partitioning to aerial

parts of Urochloa sp. and P. glaucum speciesenables a different management, sinceU. ruziziensis species accumulate, on average,70% of the dry matter in the leaves and so itmay be more efficient at ground coverage,while P. glaucum species accumulate 60% inthe stem, which can contribute for a betterplant residue retention on the soil. Accordingly,

Table 2 - Dry matter of cover crops in desiccation management

Means followed by the same letter, lower case letter in the column and capital letter in the line, are not significantly different by Scott-Knott test at 5% probability. ns non-significant. DAE – days after soybean emergence. DAD – days after desiccation management.

Table 3 - Ground coverage regarding herbicide application on cover crops in desiccation management. Sinop-MT, 2013/2014


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the highest ground coverage rate allows abetter weed control (Goulart et al., 2009;Pacheco et al., 2013b).

There was no significant effect ofherbicides in desiccation management ofcover crops on dry matter, height andphytotoxicity of soybean plants at 7, 14 and28 DAE (Tables 4, 5 and 6). These resultscorroborate those obtained by Brighenti et al.(2002) and Barros et al. (2005), who found noeffect of imazaquin herbicide on soybeangenotypes when the recommended dose(160 g ha-1) was used. A significant effect onplant height was observed, but only on coverplants, especially C. spectabilis, whichdisplayed the highest values, regardless ofevaluation period. This result can be assignedto the ability of nitrogen fixation of this species,that in some way may have contributed toreduce nitrogen immobilization in the soil,since predecessors cultivation remains hadcome from plants with a mechanism of C4carbon fixation and, therefore, with a high C/N ratio. Thus, the increased availability of Nin the soil to plants may have contributed tothis greater initial growth.

Although imazaquin herbicide isrecommended for post-emergence soybeancultivation, there was a concern about possibletoxic effects on soybean plantations. However,in the specialized literature such effectshave been observed with greater intensitywhen applied in a higher dose than thatrecommended. These results are importantbecause they open up new options for theuse of herbicides combined with glyphosatein desiccation management, aiming atcontrolling volunteer RR® corn in soybeancrops.

Except a single application of glyphosatein desiccation management, other herbicidesprovide significant volunteer RR® corn controlderived from desiccation (Table 7). We haveobserved that, in general, a better control at35 and 49 DAA was found in glyphosate +haloxyfop-R treatment and it could be a goodalternative for volunteer RR® corn controlupon desiccation. In this case, as the covercrops were planted after the RR® corn harvestfrom the previous season, no effects onvolunteer RR® corn germination and earlydevelopment were observed.

Table 4 - Soybean dry matter under cover crops and herbicides in desiccation management. Sinop-MT, 2013/2014

ns non-significant. DAE – days after soybean emergence.



It is important to mention that, besidesthe expected effects of graminicidalhaloxyfop-R and fluazifop-p-butyl mixed withglyphosate for RR® corn control, glyphosate +imazethapyr mixture also provided satisfactorycontrol (> 80%) when used in desiccationmanagement. A satisfactory control togetherwith the use of glyphosate + imazethapyrbecomes an important tool for volunteer RR®corn management, since it is a mixture well-known by producers and technicians, howeverit is necessary to use an imazethapyr full dose(0.1 kg ha-1).

Another important aspect is thatimazethapyr herbicide at a dose of 0.1 kg ha-1

shows a residual effect, aiming at the controlof volunteer RR® corn derived from emergencefluxes subsequent to desiccation management(Table 8). Imazaquin herbicide (0.16 kg ha-1)also displayed a residual effect that providessatisfactory control of volunteer RR® cornderived from emergence fluxes subsequent todesiccation management; nonetheless, itpresents a lower maize plants control at thetime of drying when compared to imazethapyr(Table 6). Residual effects of imazethapyr and

Table 5 - Height of soybean plants under cover crops and herbicides in desiccation management. Sinop-MT, 2013/2014. Sinop-MT,2013/2014

Means followed by the same capital letter in the line are not significantly different by Scott-Knott test at 5% probability. ns non-significant.DAE – days after soybean emergence.

Table 6 - Phytotoxicity in soybean plants under cover crops and herbicides in desiccation management. Sinop-MT, 2013/2014

ns non-significant. DAE – days after soybean emergence.

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imazaquin up to 60 days after application onmaize plants were also verified by Artuzi &Contiero (2006). However, these researchersdid not find any effect on corn when it wasplanted after 60 DAA. Dan et al. (2012) havefound little residual effect of imazethapyr inmaize plants at 97 DAA.

Divergent responses regarding sensitivityof maize to imazethapyr are due to genetic

variability present in different cultivars(Abit et al., 2009), the physico-chemicalcharacteristics of the herbicide and the soil(microbiological) and the ecological conditionsof region (Oliveira Jr. et al., 1999). In general,researches (Artuzi & Contiero, 2006; Danet al., 2012; Souto et al., 2013) show anabsence of imazethapyr residual effects from90 DAA. Based on these results, maizecultivation in the off-season after application

Table 7 - Control of maize in desiccation under cover crops and herbicides in desiccation management. Sinop-MT, 2013/2014

Means followed by the same lower case letter in the column are not significantly different by Scott-Knott test at 5% probability. ns non-significant. DAA – days after application in desiccation management.

Table 8 - Control of volunteer corn derived from emergence fluxes subsequent to desiccation management under cover crops andherbicides at the onset of soybean flowering. Sinop-MT, 2013/2014




of glyphosate + imazethapyr for soybeandesiccation management is completely viable,because one would have a period of not lessthan 100 DAA, even with precociuos soybeancultivars. However, it would be important toquantify the persistence of this herbicide inthe soil and climate conditions of that region,considering that the half-life of herbicides insoils depends on the chemical and physicalcharacteristics, as well as the soil microbialactivity. In this sense, Souto et al. (2013)found 93% imazethapyr degradation in soybeanrhizosphere soil at 63 DAA. According to thoseauthors, imazethapyr degradation is greaterin soils cultivated with plant species as theyprovide a more favorable environment formicrobial activity. Thus, the use of cover cropswith herbicide management, besides helpingcontrol volunteer RR® corn, can reducepossible residual and phytotoxic effects ofherbicides on corn crops in the subsequentoff-season.

U. ruziziensis cultivation assistedin controlling volunteer RR® corn inapproximately 25%, which can be verified intreatments without the use of herbicidesthat display residual effects (Table 8). Whenwe applied herbicides glyphosate andimazethapyr under U. ruziziensis, the controlof volunteer RR® corn derived from fluxessubsequent to desiccation management wasabove 80%, keeping the crop free from RR®corn throughout the critical period ofinterference prevention. Morphological andphysiological characteristics of U. ruziziensisallow a greater ground coverage and,consequently, a higher suppressive effect onvolunteer RR® corn derived from fluxessubsequent to desiccation. U. ruziziensis drymatter effect and ground coverage rate on

weeds was also reported by Pacheco et al.(2013b), becoming more evident when theresidual disposal rate was above 4.0 t ha-1. Inthe present experiment, U. ruziziensis drymatter rate was approximately 6.0 t ha-1,explaining its effect on RR® corn earlydevelopment.

We did not find any effects (p>0.05) ofherbicide managements and cover crops onsoybean yield (Table 9). These data are similarto those obtained by Artuzi & Contiero (2006),who also found no effect of imazethapyr andimazaquin in soybeans. The absence ofgraminicidal effects was expected, since theyare totally selective herbicides for soybeancrops.

However, it is possible to notice a reducedproductivity in glyphosate treatments,glyphosate + haloxyfop-R and glyphosate +fluazifop-p-butyl, when compared to glyphosatetreatments glyphosate + imazethapyr andglyphosate + imazaquin, and this can be dueto interspecific competition between volunteerRR® corn and soybean. Another aspect toconsider is that, even with no significantreduction (p>0.05) in productivity, the presenceof volunteer RR® corn amid soybean cropsat the time of mechanical harvesting canadversely affect the grain moisture andincrease the amount of impurities.

The results demonstrate that thecombined application of glyphosate andimazethapyr in desiccation managementassociated with cover crops, such asU. ruziziensis allows a satisfactory control ofvolunteer RR® corn present at the desiccationand derived from emergence fluxes subsequentto that period, without adversely affectingsoybean yields. The advantage of using this

Tabela 9 - Soybean yield under cover crops and herbicides in desiccation management. Sinop-MT, 2013/2014

ns non-significant by Scott-Knott test at 5% probability.

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management is that imazethapyr herbicide(ALS inhibitor) not only provide an effectivecontrol of volunteer corn, but also of broadleafweeds. Another option for volunteer cornmanagement in soybean crops is desiccationmanagement with glyphosate + haloxyfop-Rand, in case of fluxes subsequent to desiccationmanagement, a post-emergence application ofhaloxyfop-R.

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